Background: Transgender adults (?trans persons?) comprise 0.6% of the United States population. The few studies that have characterized the care received by trans persons have used relatively small and non- representative samples. There is a need to know more about the care that trans persons currently receive, as a basis for improving this care in the future. Approach: We will use a database containing approximately 160 million people, which is broadly representative of commercially insured people in the United States. In our pilot analyses, we identified 9,632 trans persons in this database, based solely upon diagnosis codes for gender dysphoria. Our project will have three aims. First, we will use a more comprehensive approach to identify trans persons in the dataset, including additional diagnosis codes, procedure codes, prescription fills, and inconsistencies in the gender variable. Second, having identified a population of trans persons, we will characterize the care they receive. We have identified four prominent clinical practice guidelines for trans care. Using these guidelines, we will identify important aspects of transgender care that are amenable to being characterized using a large database. As an example, we will characterize the adequacy of laboratory monitoring in patients receiving transgender hormone therapy. We have already identified at least fourteen aspects of care to study. In finalizing our list of analyses, and operationalizing how we will analyze them, we will be advised by a panel of clinical experts. For each analysis, we will define a denominator, or a group of patients eligible to receive that care element, and a numerator, a subset of the denominator who did receive it. We will calculate the proportion of patients who received each care element, and examine differences between subgroups (e.g., male vs. female gender identity, age, race). Third, we will convene a panel of seven clinical experts in trans care, as well as three trans patients. Using our results, this technical expert panel (TEP) will help advise us regarding which analyses would be potentially suitable to serve as a basis for developing quality of care metrics for trans patients. TEP members will be asked to comment on four aspects of potential quality measures: 1) importance; 2) reliability and validity; 3) ease of understanding; and 4) feasibility of collection and calculation. Anticipated Impacts: This study will constitute the largest study to characterize the care delivered to trans persons to date, and the results will be generalizable to the US population of commercially insured individuals. The methods we develop to identify trans persons in a large, automated database will serve as a basis for future studies by our group and by others. In addition to providing a baseline for the quality of care delivered to trans persons today, our results and the input from our TEP will provide a basis for the future development of quality measures for trans care. The existence of such quality measures has the potential to facilitate quality improvement over time.